IB›IB Chemistry SL›Mind mapsR1.1 Measuring enthalpy changesIB Chemistry SL: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsEnergy basicsSystem: reacting chemicalsSurroundings: everything elseHeat is energy transferred, in JTemperature is average kinetic energyExo and endoExothermic: surroundings warm, ΔH negativeEndothermic: surroundings cool, ΔH positiveProducts more stable: energy releasedCombustion and neutralisation are exothermicDissolving NHX4NOX3\ce{NH4NO3}NHX4NOX3 is endothermicEnergy profilesExothermic: products below reactantsEndothermic: products above reactantsHump height is activation energyEndothermic: EaE_aEa is larger than ΔHEnthalpymeasuring changesΔHkJJKStandard ΔHConstant pressure heat transferStandard: 100 kPa, 1 mol dm⁻³, 298 KGiven per mole, in kJ mol⁻¹CalculatingQ=mcΔTQ = mc\Delta TQ=mcΔTc=4.18 J g−1K−1c = 4.18\,\text{J g}^{-1}\text{K}^{-1}c=4.18J g−1K−1 for waterΔH=−Qn\Delta H = -\frac{Q}{n}ΔH=−nQ in kJHCl + NaOH, 6.6 K rise: −55.2 kJ mol⁻¹Exam tipsUse total mass of solution for mmmExperiments are less exothermic: heat lossFuels: incomplete combustion, evaporationInsulate, add a lid and stirThermometer reads surroundings, not system